Method for Monitoring the Operability of a Fuel Injection System

ABSTRACT

A method for monitoring the operability of injection system of an internal combustion engine is described whereby, if the quantity of fuel injected changes, a malfunction source is detected according to the behavior of the pressure obtaining in the high-pressure accumulator. An appropriate emergency control program is executed by the control unit depending on the malfunction source detected. The method describes enables a malfunction source to be simply and accurately analyzed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national stage application of InternationalApplication No. PCT/EP2006/050334 filed Jan. 20, 2006, which designatesthe United States of America, and claims priority to German applicationnumber DE 10 2005 004 423.9 filed Jan. 31, 2005, the contents of whichare hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The invention relates to a method for monitoring the operability of afuel injection system according to claim 1.

BACKGROUND

A wide variety of methods for monitoring the operability of a fuelinjection system are known from the prior art. The increasinglystringent exhaust gas regulations require ever more precision from thefuel injection systems of internal combustion engines. The requirementsplaced on the methods for monitoring the operability of fuel injectionsystems are therefore also becoming more exacting.

DE 198 56 203 C2 discloses a fuel supply system for an internalcombustion engine of a motor vehicle whereby fuel is delivered to apressure accumulator by a pump. Connected to the pressure accumulatorare injection valves which supply fuel to the internal combustion enginewhen activated by a control unit. To monitor the operability of the fuelsupply system, the pressure in the pressure accumulator is caused tochange by the control unit. The time required to set the pressure changeis then measured. The time measured is compared with experimentallydetermined time values and a fault is deemed to be present if themeasured time values do not correspond to the stored time values.

In addition, DE 199 46 506 C1 discloses a method for monitoringmalfunctions in the pressure system of a fuel injection system bymeasuring the pressure change in the pressure system and determiningperiodic pressure variations. A fault is indicated if the periodicity ofthe registered pressure measuring signal deviates significantly from thepattern to be expected for fault-free operation of the system in respectof the amplitude and/or homogeneity of the pressure variations.

SUMMARY

The object to the invention is to provide an improved method formonitoring the operability of a fuel injection system.

This object can be achieved by a method for monitoring the operabilityof an injection system of an internal combustion engine, comprising apressure accumulator, an injection valve connected to the pressureaccumulator, a controllable fuel supply system which delivers fuel tothe pressure accumulator, the method comprising the steps of: measuringthe pressure in the pressure accumulator by a pressure sensor coupledwith the pressure accumulator, feeding the measured pressure value to acontrol unit; controlling the quantity of fuel delivered by theinjection valve and supplied from the fuel supply system as a functionof operating parameters of the internal combustion engine, varying thequantity of fuel delivered by the injection valve, measuring a resultingpressure, comparing the resulting pressure with a setpoint pressure forthe given operating conditions, and detecting a malfunction sourcedepending on the deviation of the measured resulting pressure from thecomparison value and if the measured resulting pressure is below thesetpoint value.

The method has the advantage that the cause of the fault is analyzed andits source is able be determined more precisely.

In another embodiment of the invention, the leak-tightness of theinjection system is detected as the malfunction source if, in the eventof a change in the injection quantity, the pressure in the pressureaccumulator is less than the setpoint value and a constant pressureestablished itself in the pressure accumulator. This means that leaks inthe pressure system of the injection system can be accurately detected,thereby enabling appropriate emergency programs to be executed by thecontrol unit.

In a further embodiment of the method according to the invention, thefuel supply is detected as the malfunction source if the injectionquantity changes and the pressure in the pressure accumulator is belowsetpoint and the fuel pressure in the pressure accumulator changescontrary to the change in the injection quantity. Thus monitoring of thefuel supply system can be performed using the described method and if afuel supply system malfunction is detected, an appropriate emergencyprogram can be employed by the control unit.

In a further preferred embodiment, the pressure in the pressureaccumulator is detected for a period of one second after a change in theinjection quantity and the pressure measured during the measurement timeis compared with a setpoint value or setpoint response. Due to thecomparatively long time period, transient faults due e.g. to defectiveinjection valves can be averaged out. This means that only faults causedby the injection system and not by the injection valves are detected.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be explained in greater detail with reference tothe accompanying drawings in which:

FIG. 1 schematically illustrates a fuel injection system;

FIG. 2 shows two diagrams the detecting a first fault scenario; and

FIG. 3 shows two diagrams the detecting a second fault scenario.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a fuel injection system for an internalcombustion engine, in particular a common rail injection system. Theinjection system has a high pressure accumulator 1 which is connected tothe injection valves 2. The high-pressure accumulator 1 is additionallyconnected to a fuel supply system 4 via a supply line 3. The fuel supplysystem is connected to a fuel tank 5. There is additionally provided acontrol unit 6 which controls the fuel supply system 4 and the injectionvalves 2 as a function of operating conditions of an internal combustionengine. For this purpose the control unit 6 has a data memory 7 in whichappropriate control programs are stored. To control the fuel supplysystem 4 there is provided a control line 11 between the control unit 6and the fuel supply system 4. In addition, sensors 9 which detect theoperating conditions of the internal combustion engine 8 are disposed onthe internal combustion engine 8. The operating conditions thusdetermined, such as the engine speed and gas pedal position, are passedto the control unit 6. Control lines for controlling the injectionvalves 2 are additionally implemented between the injection valves 2 andthe control unit. There is additionally provided on the high-pressureaccumulator 1 a pressure sensor 10 which detects the fuel pressure inthe high-pressure accumulator 1 and forwards it to the control unit 6.

The task of the fuel supply system 4 is to supply the high-pressureaccumulator 1 with fuel at a desired setpoint pressure under the controlby the control unit 6. For this purpose the fuel supply system 4 canhave various components. In the embodiment shown, the fuel supply system4 has a fuel pump 12 and a meter-in flow control valve 13 connectedbetween the fuel tank 5 and the fuel pump 12. Between the fuel pump 12and the high-pressure accumulator 1 there is additionally connected apressure valve 14 whose output is connected to a return line 15.

For controlling the amount of fuel supplied to the high-pressureaccumulator 1, a flow cross section of the meter-in flow control valve13 is increased to a lesser or greater degree by the control unit 6 sothat a larger or smaller amount of fuel can be delivered to thehigh-pressure accumulator 1 by the fuel pump 12. Additionally availableas a further means of influencing the fuel pressure in the high-pressureaccumulator 1 is the pressure valve 14 which is likewise actuated by thecontrol unit 6. If the pressure valve 14 is caused to open by thecontrol unit 6, fuel which has already been compressed by the fuel pump12 and pumped into the supply line 3 is fed back into the fuel tank 5via the return line 15, thereby reducing the fuel pressure in thehigh-pressure accumulator 1.

During operation of the internal combustion engine, the fuel supply tothe high-pressure accumulator 1, the fuel pressure in the high-pressureaccumulator 1 and the quantity of fuel delivered by the injection valves2 is adjusted according to defined control programs as a function ofoperating conditions of the internal combustion engine 8.

The pressure at which the fuel is injected is an essential criterion forthe exhaust quality of the internal combustion engine and must thereforebe precisely adhered to.

FIG. 2 (top) shows the time response of the quantity of fuel deliveredby the injection valves 2. The lower diagram plots the parallel timeresponse of the pressure in the high-pressure accumulator 1 which isdetected by the pressure sensor 10. The top diagram shows that thequantity of fuel at instant t0 falls from an upper value to a lowervalue at instant t1 and then increases again to a higher value atinstant t2, falling again to a lower value at instant t3. The timebetween the 0^(th) instant t0 and the third instant t3 is longer than 1second.

In parallel with this, the lower diagram plots both the setpoint valueof the fuel pressure and the measured pressure p over time. The setpointis specified by the control program depending on operating conditions ofthe internal combustion engine. The control unit 6 activates the fuelsupply system 4 such that the setpoint pressure is set. The lowerdiagram shows that during the measuring period, i.e. from the 0^(th)instant t0 to the third instant t3, the pressure value p measuredremains virtually constant and is below the setpoint pressure.

The control unit 6 therefore detects that a malfunction is present inthe fuel supply system 4. The control unit 6 can also detect on thebasis of the existing situation, i.e. the injected fuel quantity changesover time and the fuel pressure obtaining in the high-pressureaccumulator 1 remains virtually constant and below setpoint, that apressure valve malfunction is present. For the detection of a virtuallyconstant pressure, a pressure range of e.g. 3% is specified within whichthe fuel pressure in the high-pressure accumulator 1 may vary duringmeasurement, the control unit 6 nevertheless detecting a constant fuelpressure in the high-pressure accumulator 1, however.

If the control 6 detects a fault in the pressure valve 14, anappropriately prepared emergency program is used by the control unit 6for the subsequent activation of the fuel supply system 4 and/orinjection valves 2. The emergency program is stored in the memory 7 ofthe control unit 6.

FIG. 3 shows another fault scenario. FIG. 3 again shows the variation inthe amount of fuel injected by the injection valves 2 over time. In thelower diagram, the setpoint value of the fuel pressure and the measuredfuel pressure are simultaneously plotted over time. Also in thissituation the quantity of fuel injected by the injection valves 2 isreduced from a high value at instant t0 to a lower value at the firstinstant t1, then increased to a higher value at the second instant t2whereupon it is reduced to a lower value at the third instant t3. Thetime between the 0^(th) instant t0 and the third instant t3 correspondsto approximately 1 second.

The time response of the measured pressure in the high-pressureaccumulator 1 exhibits a pressure variation contrary to the fuelvariation, i.e. while the amount of fuel injected is falling, the fuelpressure in the high-pressure accumulator 1 is increasing and viceversa. The control unit 6 therefore unambiguously detects a malfunctionof the meter-in flow control valve 13. If a malfunction of the meter-inflow control valve 13 is detected, an appropriate emergency program forthe subsequent activation of the supply system 4 and/or the injectionvalves 2 is employed by the control unit 6.

For example, the emergency program used in the event of a meter-in flowcontrol valve malfunction reduces the quantity of fuel to be injected bythe injection valves 2. If a defective pressure valve is detected, thepressure setpoint value is additionally limited, for example.

Other parameters for the emergency program to be used can be limited orvaried depending on the application.

1. A method for monitoring the operability of an injection system of aninternal combustion engine, comprising a pressure accumulator, aninjection valve connected to the pressure accumulator, a controllablefuel supply system which delivers fuel to the pressure accumulator, themethod comprising the steps of: measuring the pressure in the pressureaccumulator by a pressure sensor coupled with the pressure accumulator,feeding the measured pressure value to a control unit; controlling thequantity of fuel delivered by the injection valve and supplied from thefuel supply system as a function of operating parameters of the internalcombustion engine, varying the quantity of fuel delivered by theinjection valve, measuring a resulting pressure, comparing the resultingpressure with a setpoint pressure for the given operating conditions,and detecting a malfunction source depending on the deviation of themeasured resulting pressure from the comparison value and if themeasured resulting pressure is below the setpoint value.
 2. The methodaccording to claim 1, wherein, if the injection quantity changes, if thepressure is below setpoint in the pressure accumulator, and in case ofan approximately constant pressure in the pressure accumulator, apressure valve connected to the pressure accumulator which cannot setthe desired pressure is detected as the source of the fault.
 3. Themethod according to claim 1, wherein, if the injection quantity changes,if the pressure is below setpoint in the pressure accumulator, and ifthe pressure in the pressure accumulator changes contrary to the changein the injection quantity, the fuel supply system which does not supplysufficient fuel is detected as the source of the fault.
 4. The methodaccording to claim 1, wherein, the pressure is measured over a measuringperiod of 1 second and the time response of the pressure during themeasuring period is compared with a setpoint response.
 5. The methodaccording to claim 1, wherein, depending on the fault detected, anappropriate emergency program for control by the control unit is used,wherein appropriate emergency programs being available to the controlunit for the various malfunctions.
 6. A method for monitoring theoperability of an injection system of an internal combustion engine,comprising the steps of: measuring the pressure in a pressureaccumulator by a pressure sensor, controlling the quantity of fueldelivered by an injection valve and supplied from a fuel supply systemas a function of operating parameters of the internal combustion engine,varying the quantity of fuel delivered by the injection valve, measuringa resulting pressure, comparing the resulting pressure with a setpointpressure for the given operating conditions, and detecting a malfunctionsource depending on the resulting pressure and on the deviation of theresulting pressure from the comparison value.
 7. The method according toclaim 6, wherein, if the injection quantity changes, if the pressure isbelow setpoint in the pressure accumulator, and in case of anapproximately constant pressure in the pressure accumulator, a pressurevalve connected to the pressure accumulator is detected as the source ofthe fault.
 8. The method according to claim 6, wherein, if the injectionquantity changes, if the pressure is below setpoint in the pressureaccumulator, and if the pressure in the pressure accumulator changescontrary to the change in the injection quantity, the fuel supply systemis detected as the source of the fault.
 9. The method according to claim6, wherein, the pressure is measured over a measuring period of 1 secondand the time response of the pressure during the measuring period iscompared with a setpoint response.
 10. The method according to claim 6,wherein, depending on the fault detected, an appropriate emergencyprogram for control by the control unit is used, wherein appropriateemergency programs being available to the control unit for the variousmalfunctions.
 11. A system for monitoring the operability of aninjection system of an internal combustion engine, comprising: apressure accumulator, an injection valve connected to the pressureaccumulator, a controllable fuel supply system which delivers fuel tothe pressure accumulator, a pressure sensor coupled with the pressureaccumulator, a control unit controlling the quantity of fuel deliveredby an injection valve and supplied from a fuel supply system as afunction of operating parameters of the internal combustion engine, andvarying the quantity of fuel delivered by the injection valve, acomparator comparing the resulting pressure with a setpoint pressure forthe given operating conditions, and detecting a malfunction sourcedepending on the resulting pressure and on the deviation of theresulting pressure from the comparison value.
 12. The system accordingto claim 11, wherein, if the injection quantity changes, if the pressureis below setpoint in the pressure accumulator, and in case of anapproximately constant pressure in the pressure accumulator, a pressurevalve connected to the pressure accumulator is detected as the source ofthe fault.
 13. The system according to claim 11, wherein, if theinjection quantity changes, if the pressure is below setpoint in thepressure accumulator, and if the pressure in the pressure accumulatorchanges contrary to the change in the injection quantity, the fuelsupply system is detected as the source of the fault.
 14. The systemaccording to claim 11, wherein, the pressure is measured over ameasuring period of 1 second and the time response of the pressureduring the measuring period is compared with a setpoint response. 15.The method according to claim 11, wherein, depending on the faultdetected, an appropriate emergency program for control by the controlunit is used, wherein appropriate emergency programs being available tothe control unit for the various malfunctions.